Static electricity

The Daleks used static electricity in their city on Skaro; rather than use an internal power source, they picked up power through the floor. The First Doctor, Ian Chesterton, Barbara Wright and Susan Foreman realised this by the smell they made when moving and were reminded of dodgems at a fairground. They disabled a Dalek by pushing it onto a Thal cloak, insulating the Dalek base from the electricity. They then used the empty Dalek shell to escape the city. (TV: The Daleks)

On Vulcan, scientist Lesterson found a capsule in a mercury swamp containing three dormant Daleks, which he brought back to life. The Vulcan colony did not have metal floors from which the Daleks could extract static electricity, so they had power cables laid for them to use. (TV: The Power of the Daleks)

While never explicitly stated that the Daleks evolved beyond a need for static electricity, later stories would drop this aspect. In addition, TV: Death to the Daleks would state that the Dalek casing was powered by the Dalek creature's telekinesis.